In both new building constructions and renovation projects, there is an increasing demand in the residential, commercial and public building construction industries to provide private homes, businesses such as shops and restaurants, and public park facilities with deck structures. These structures typically comprise joists overlain with planks or floor boards and bound by a plurality of posts. Because of its natural beauty, comparatively low cost and abundant supply, wood has historically been the predominant material of choice in the construction of decks and similar structures, e.g., walkways, steps, and boat decks and piers. However, the lumber used in the construction of such structures requires considerable and costly maintenance to slow its inevitable deterioration caused by continual exposure to the sun, rain, snow and other natural elements. Moreover, wooden decks and related structures are subject to splintering which can be a hazard to individuals in bare feet. And, wooden structures are highly flammable.
For these and other reasons, rigid plastics such as polyvinyl chloride (PVC) have become an increasingly popular alternative to wood in the construction of decks and similar structures. Examples of deck systems fabricated in whole or in part from rigid plastic include those disclosed in U.S. Pat. Nos. 5,048,448, 5,009,045 and Des. 329,914 (which are all expressly incorporated by reference herein), as well as certain systems marketed by PVC Design of Fort Lauderdale, Fla., Thermal Industries, Inc. of Pittsburgh, Pa., Royal Group Technologies Limited of Ontario, Canada, L.B. Plastics, Inc. of Mooresville, N.C., Brock Manufacturing of Milford, Ind., Heritage Vinyl Products of Macon, Miss., Alside, Inc. of Akron, Ohio, PVC Lumber System of Montreal, Canada and Vecor Enterprises Inc. of Chomedey Laval, Canada. Most of these systems comprise extruded plastic, e.g., PVC, decking planks and end caps. According to some of these designs the flooring planks are secured to fastener strips which in turn are secured to the joists. In others, such as the PVC Lumber System and Vecor Enterprises Inc. designs, the decking planks are secured directly to the joists via screws or similar fastening means.
The profiles of the PVC Lumber System and Vecor Enterprises Inc. decking planks include at least one deep channel in the upper surface of and extending longitudinally along the planks. The screws are inserted into the channel and driven therethrough and into the joists to anchor the plank to the joists. Once the screws have been installed, an elongated plastic cover, typically formed from PVC, is inserted into the channel to cover the screw heads and give a finished appearance to the plank. On its substantially vertical side walls the channel is provided with at least one pair of opposed ledges extending the length of the recess. The PVC screw cover has upper and lower flanges which project from both of its longitudinal side edges. The flanges are spaced apart a distance sufficient to closely receive one pair of the opposed ledges, i.e., with a gap of about 0.010 to about 0.020 inch. With such a tight gap the screw cover has little room to move outwardly with respect to the ledges under the influence of expanding ice that may form in the channel. Consequently, the lower flanges of the screw cover are especially susceptible to shear failure. That is, the lower flanges may snap under the potentially great compressive contact force that can arise between the lower flanges and the lower surfaces of the captured ledges as a result of ice expansion in the channel. Such failure may entail costly and time consuming replacement of the screw cover depending upon the extent of the damage. And, even if the screw cover flanges do not break, the screw cover may nevertheless be expelled from the channel and may not be reinserted therein until the channel ice is sufficiently thawed.